JavaScript getElementById() Method

You can use the JavaScript getElementById() method to get an element with a specified id. This is one of the most commonly used methods in JavaScript. We often use this method extract information about an element or manipulate the contents of an element.

Syntax of getElementById() Method

document.getElementById(element_id);

It’s a method of the document object. The method takes a parameter in the form of an element’s id. For example, if you have a paragraph element on your web page, which also have an id, your code should look like this.

<html>
<body>
    <p id="msg">This is a paragraph.</p>
</body>
<script>
    const msg = document.getElementById('msg');    // Get the element with id "msg".
    document.write(msg);        // Write the element's property.
</script>
</html>
Try it

The name of the method is case-sensitive. So, be careful when you are typing the method. For example, By cannot be by or Id cannot be ID. However, most JavaScript editors today have in-built intellisense or intelligent code completion feature. Therefore, you need not to worry.

Please make sure the ID’s you assign to the elements on your web page are unique. No element should have the same id.

Here’s an example.

<html>
<head>
    <title>JavaScript getElementById() Method Example</title>
</head>
<body>
    <div>
      <input type='text' id='your_name' placeholder='Enter your name' />
      <input type='button' value='Click it' id='bt' onclick='say_hello()' />
    </div>

    <p id="msg"></p>
</body>
<script>
    let say_hello = () => {
        let name = document.getElementById('your_name').value;
        let msg = document.getElementById('msg');
        msg.innerHTML = 'Hello ' + name + ' ☺';
	}
</script>
</html>
Try it

In the above example, I have four different elements. Out of which only 3 have ids and all are unique.

In the <script> section, I have used the getElementById() method twice:

The first method has the id (your_name) of an input box of type text. I am using the method with another property called value, to extract the value of the input box.

The second method has the id of a <p> element. Here, I am actually manipulating or changing the content of the element.

Same method, different purpose

Remember, if you have assigned an id to the getElementById() method that does not exist in your web page, then it will return a null. In this case, the browser’s console window will show you an error. For example,

<html>
<body>
    <p>
        See the console window (Shift+Ctrl+i) for the error.
    </p>
    
    <div id="container">
        
    </div>
</body>
<script>
    let cont = document.getElementById('container1');   // The id container1 does not exist.
    cont.innerHTML = 'Hello!';          // So, it will throw an error here.
</script>
</html>
Try it
Conclusion

The JavaScript getElementById() is a very useful method. You might have to use it in almost all your web applications. It’s a method of the document object. Therefore, you have to always use it like this: document.getElementById(element_id). Or else, the browser will throw an error saying,

Uncaught ReferenceError: getElementById is not defined

Be careful with the capitalization part of the method. It is case-sensitive.

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